Atomistic and phase field simulations of three dimensional interactions of {10(1)over-bar2} twins with grain boundaries in Mg: Twin transmission and dislocation emission

In polycrystals, the interaction of dislocations and twins with grain boundaries (GBs) plays a role in hardening and formability during plastic deformation. While dislocation-GB interactions are relatively well-understood, twin-GB interactions remain mostly unknown. Here, an approach using molecular dynamics and phase-field simulations is followed to study the forward and lateral interactions between {10 (1) over bar2} twins and tilt grain boundaries in Mg. Molecular dynamics results show that the resolved shear stress on slip/twinning modes of the neighboring grain, not the geometric alignment, is the dominant factor in determining the outcome of the twin-GB interactions. For some lateral interaction configurations, as the misorientation angle increases, the resolved shear stress on the same {10 (1) over bar2} twin variant of the neighboring grain reduces while it increases for slip or I-2 stacking fault emissions or other twin modes such as {11 (2) over bar1} and {10 (1) over bar1}, explaining why twin transmission is not seen at high misorientation angles. Furthermore, lateral and forward interactions of the twin with tilt grain boundaries whose misorientation axes are normal to the coherent twin boundary show significantly different outcomes. For the forward interaction, the twin is absorbed and stacking faults are emitted when interacting for low misorientation angles (up to 30 degrees) while the lateral interaction results in twin transmission, nucleation of a {11 (2) over bar1} twin, and emission of I-2 stacking faults. Finally, comparisons between twin interactions with symmetric and asymmetric tilt GBs with different GB structures show similar outcomes.

Automated summary

The interaction between dislocations, twins, and grain boundaries in polycrystals plays a crucial role in hardening and formability during plastic deformation. While the interaction between dislocations and grain boundaries is relatively well-understood, the interaction between twins and grain boundaries remains mostly unknown. Molecular dynamics simulations show that the shear stress on slip/twinning modes of the neighboring grain, rather than the geometric alignment, determines the outcome of twin-grain boundary interactions. As the misorientation angle increases, the shear stress on the same twin variant decreases while it increases for other twin modes, explaining why twin transmission is not observed at high misorientation angles. Additionally, interactions between twins and tilt grain boundaries with different misorientation axes show significantly different outcomes in both lateral and forward directions.